The Spanish giants managed to secure a 3-1 victory in the return leg of the Copa del Rey semi-final against their fiercest rivals at the Camp Nou last night.
"We have to transfer this to the match against Manchester United," BBC Sport quotes Casillas as saying. "It is also 1-1 and we have to score and keep a clean sheet. That's the aim that we're going with. We have to take what we have done [against Barca] to Old Trafford."
Casillas was sidelined for Madrid's first leg against United at the Bernabeu with a broken hand.